The present invention relates to methods and apparatus for eliminating thermal conduction between the exterior and interior surfaces of metal frame windows and doors, particularly aluminum frame windows and doors.
Although the preferred embodiment of this invention is described in relation to a double-hung aluminum frame window, it is to be understood that the principles described herein apply to other types of aluminum or metal windows as well as a variety of metal door structures.
A well-recognized problem concerning aluminum frame windows and doors relates to the high thermal conductivity of aluminum. The symptoms of the problem are twofold: (1) the thermal conductivity of the aluminum frame results in losses and inefficient heating or cooling of the premises interior; and (2) in cold weather there is considerable condensation on the inside of the aluminum frame, resulting in considerable mess and water damage to walls, floors, curtains, etc. There have been a number of prior art approaches to solving this problem, the most effective of which uses a thermal barrier poured to join the outside and inside frame sections. Examples of this approach are found in U.S. Pat. No. 3,204,324 to Nilsen, and U.S. Pat. No. 3,818,666 to Winans. In the Nilsen patent an extruded aluminum member is provided with a three-sided channel which is filled with a molten polyester resin of a type which is allowed to harden and adhere to the inside channel walls. Thereafter the bottom channel wall is removed by an appropriate machining process, leaving two aluminum members joined by the rigid, thermally-insulative resin. Industrial experience has proven the machining step for removal of the bottom channel wall to be an expensive and time-consuming part of the frame fabrication procedure. In addition, the resulting inside and outside frame members must be the same color, a factor which is undesirable from a consumer product viewpoint. The reason for the same color requirement is that the resulting thermally-insulated members cannot be subjected to the high temperatures required for surface curing without destroying or structurally impairing the thermal fill material. Consequently, the two frame members must remain the same color as the original single frame member.
The Winans patent recognizes the aforementioned disadvantages of the Nilsen approach and offers a structure which is formed from two individual aluminum members. The two members are placed in a jig with spaced side walls of each member forming respective sides of a channel to be filled. A U-section vinyl bridge is placed around the channel so that the base of the bridge defines the bottom of the channel and the sides of the bridge engage the outside surfaces of the channel side walls. The channel is then filled with molten resin material, as in Nilsen, and allowed to harden. Winans' approach eliminates some of the problems inherent in the Nilsen approach but not all, and it also introduces other problems. For example, Winans recesses the thermal break joint into the window jamb, so that both sides of the track for the window sash are aluminum. Therefore, in a double-hung window, one side of the aluminum track must communicate between the exterior and interior of the premises, even when the window is closed. This problem is more clearly described in the Background section hereof in relation to prior art FIGS. 1-3. The result is that a thermally conductive aluminum path communicates between the premises exterior and interior and thereby largely negates the insulative effect of the thermal break. This same problem exists in the Nilsen approach. Further, in Winans the bridge member must include projections which extend into the bottom of the filled channel to assure that the vinyl bridge remains secured to the hardened thermal fill material. Winans states that the vinyl bridge can be stripped away after the fill hardens or can be left on. In either case, the vinyl bridge is considerably more expensive than the fill material and adds considerably to the expense of the manufacturing process. This is true because even if the bridge is stripped away it cannot be re-used because the projections from the bridge into the channel must be severed during the stripping.
It is an object of the present invention to provide an aluminum frame window or door and a method for fabricating same which eliminates the aforementioned problems.
It is an object of the present invention to provide an inexpensive thermal break having improved insulating efficiency.
It is another object of the present invention to provide a method for simply and efficiently fabricating an improved thermal break.